Synthetic resin cap, closing device, and container-packed beverage

ABSTRACT

The present invention provides a synthetic resin cap comprising: a cap body ( 4 ) having a top plate portion ( 2 ) and a cylinder portion ( 3 ) hanging from a circumferential edge portion ( 2   b ) thereof; an annular inside seal projection ( 12 ) to be fitted to a container mouth portion ( 21 ); a connector portion ( 15 ) formed between the top plate portion ( 2 ) and the inside seal projection ( 12 ); and an outside thin wall portion ( 16 ) formed on the top plate portion ( 2 ), and provides a closing device using thereof, and a container-packed beverage. 
     When the internal pressure of the container has risen, the top plate portion ( 2 ) is deformably swelled upward, and an inward tensile force is applied to the inside seal projection ( 12 ) by the connector portion ( 15 ). Since the outside thin wall portion ( 16 ) undergoes bending deformation, the portion positioned inside the outside thin wall portion ( 16 ) to undergo significant bulging deformation upward, and the slope of the top plate portion ( 2 ) at the portion where the inside seal projection ( 12 ) is formed is increased. Thus, the inside seal projection ( 12 ) is displaced inward, and gas in the container may be easily discharged to the outside.

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application PCT/JP2004/011120, filed Jul. 28, 2004, whichclaims priority to Japanese Patent Application No. 2003-328992, filedSep. 19, 2003. The International Application was published under PCTArticle 21(2) in a language other than English.

TECHNICAL FIELD

The present invention relates to a synthetic resin cap that closes acontainer mouth portion, a closing device using the cap, and acontainer-packed beverage.

Priority is claimed on Japanese Patent Application No. 2003-328992, thecontent of which is incorporated herein by reference.

BACKGROUND ART

Conventionally, many conventional synthetic resin caps have been usedprovided a top plate portion and a cylinder portion hanging from thecircumferential edge thereof, with an annular inside seal projection tobe fitted into the container mouth portion protrudingly formed on theinner surface of the top plate portion (refer for example to JapaneseUnexamined Patent Application No. 2002-211605).

FIG. 6A and FIG. 6B show an example of a synthetic resin cap having aninside seal projection, the cap 31 including a cap body 4 having a topplate portion 2 and a cylinder portion 3 hanging from a circumferentialedge portion 2 b thereof.

The horizontal score 6 demarcates the cylinder portion 3 into a mainportion 8 and a tamper evidence ring portion (TE ring portion) 9connected to the main portion 8 by bridges 7.

On the inner surface of the main portion 8, a thread portion 10 isformed for threaded engagement with a male screw 22 formed on an outersurface 21 c of a container mouth portion 21.

On the inner surface of the TE ring portion 9 are provided tabs 11 thatblock movement of the TE ring portion 9 by locking to the containermouth portion when opening the cap 1.

On the inner surface 2 a of the top plate portion 2 is formed an annularinside seal projection 12 to be fitted into the container mouth portion21. On the outer surface of the tip portion of the inside sealprojection 12 is formed an annular abutting convex portion 12 a to abutthe container inner surface 21 a.

On the top plate portion 2 are formed an opening end seal projection 13to abut an opening end face 21 b of a container mouth portion 21 and anoutside seal projection 14 to abut the outer surface 21 c of thecontainer mouth portion 21.

DISCLOSURE OF THE INVENTION

When the cap is opened and then closed again (hereafter, recapped), theinternal pressure of the container increases due to fermentation of thecontent liquid and the like, in which case there has been the problem ofthe cap readily coming off the container.

For this reason, technology has been desired that can discharge gas inthe container to the outside to lower the internal pressure of thecontainer when the internal pressure of the container has risen afterrecapping.

The present invention was achieved in view of these circumstances, andhas as its object providing a synthetic resin cap that can prevent anexcessive increase in the internal pressure of a container when the capis opened and then closed again, a closing device and a container-packedbeverage.

The synthetic resin cap of the present invention is characterized byincluding a cap body having a top plate portion and a cylinder portionhanging from a circumferential edge portion thereof, an annular insideseal projection to be fitted into a container mouth portion being formedon an inner surface of the top plate portion, a connector portion thatconnects the top plate portion and the inside seal projection beingformed between the inner surface of the top plate portion and an innersurface of the inside seal projection, and an outside thin wall portionformed thinner than the circumferential edge portion being formed on thetop plate portion at any position between a portion where the insideseal projection is formed and the circumferential edge portion.

In the synthetic resin cap of the present invention, a cross-sectionalradius of curvature at an inner surface side of a junction portion ofthe top plate portion and the cylinder portion is preferably not lessthan 0.6 mm.

In the synthetic cap of the present invention, the top plate portion atthe portion corresponding to inside of the inside seal projection has anouter circumferential side portion where the connector portion is formedand an inside thin wall portion that is formed to the inside of theouter circumferential side portion, with the inside thin wall portionpreferably being formed thinner than the outer circumferential sideportion.

A thickness of the outer circumferential side portion is preferably 0.5mm to 3 mm.

A width of the outer circumferential side portion is preferably 0.5 mmto 10 mm.

In the synthetic resin cap of the present invention, when attached tothe container mouth portion, it is preferable that a distance between aninner surface of the cylinder portion and a tip of a male screw formedon an outer surface of the container mouth portion be not more than 1mm.

In the synthetic resin cap of the present invention, when attached tothe container mouth portion it is preferable that a distance between atip of a thread portion formed in the cylinder portion and the outersurface of the container mouth portion be not more than 1 mm.

In the synthetic resin cap of the present invention, it is preferablethat an opening end seal projection to abut an opening end face of thecontainer mouth portion be formed on the top plate portion.

In the synthetic resin cap of the present invention, it is preferablethat the inside seal projection be made to abut the inner surface of thecontainer mouth portion at a maximum outer diameter portion and that theheight position of the maximum outer diameter portion be set so that thedifference in height of the maximum outer diameter portion and thebottom end of the opening end seal projection is 1 mm to 4 mm.

In the synthetic resin cap of the present invention, it is preferablethat an outside seal projection to abut the outer surface of thecontainer mouth portion be formed on the top plate portion and that theoutside seal projection be formed so that the difference in height ofthe bottom end of this projection and the bottom end of the opening endseal projection is not more than 3 mm.

It is preferable that the flexural modulus of the top plate portion be500 to 2,000 MPa.

It is preferable that the density of the material constituting thesynthetic resin cap be 0.85 to 0.97 g/cm³.

The closing device of the present invention is characterized byincluding a container and a synthetic resin cap attached to a mouthportion thereof, the synthetic resin cap including a cap body having atop plate portion and a cylinder portion hanging from a circumferentialedge portion thereof, an annular inside seal projection to be fittedinto the container mouth portion being formed on an inner surface of thetop plate portion, a connector portion that connects the top plateportion and the inside seal projection being formed between the innersurface of the top plate portion and the inner surface of the insideseal projection, and an outside thin wall portion thinner than thecircumferential edge portion being formed at any position between theportion where the inside seal projection is formed and thecircumferential edge portion.

The container-packed beverage of the present invention is a containerpacked beverage in which a beverage is filled in a closing deviceincluding a container and a synthetic resin cap attached to the mouthportion thereof, characterized by the synthetic resin cap including acap body having a top plate portion and a cylinder portion hanging fromthe circumferential edge portion thereof, an annular inside sealprojection to be fitted into the container mouth portion being formed onthe inner surface of the top plate portion, a connector portion thatconnects the top plate portion and the inside seal projection beingformed between the inner surface of the top plate portion and the innersurface of the inside seal projection, and an outside thin wall portionthinner than the circumferential edge portion being formed on the topplate portion at any position between the portion where the inside sealprojection is formed and the circumferential edge portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross sectional view showing one embodiment of aclosing device of the present invention.

FIG. 2 is a main part enlarged view showing a synthetic resin cap of theclosing device shown in FIG. 1.

FIG. 3 is a cross sectional view showing the state of the syntheticresin cap shown in FIG. 1 attached to a container mouth portion.

FIG. 4 is a transverse cross sectional view showing the synthetic resincap shown in FIG. 1.

FIG. 5 is an enlarged view showing a main part of the synthetic resincap shown in FIG. 1.

FIG. 6A is an overall view showing an example of a conventionalsynthetic resin cap.

FIG. 6B is an enlarged view showing a main part of the state of thesynthetic resin cap shown in FIG. 6A attached to a container mouthportion.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an embodiment of a closing device of the present invention.FIGS. 2 to 4 show a synthetic resin cap used in the closing device.

The closing device shown in FIG. 1 is constituted from a container 20and a synthetic resin cap 1 attached to a mouth portion 21 thereof. Inthe explanation below, inward and outward mean inward and outward in theradial direction of the cap 1.

The container 20 may be used made of a synthetic resin such aspolyethylene terephthalate (PET), glass, metal or the like.

The cap 1 has a cap body 4 having a top plate portion 2 and a cylinderportion 3 hanging from a circumferential edge portion 2 b thereof.

The cylinder portion 3 is demarcated by a horizontal score 6 (weakeningline) into a main portion 8 from the horizontal score 6 upward and atamper evidence ring portion (TE ring portion) 9 therebelow that iscoupled to a bottom end of the main portion 8 by a plurality of finebridges 7.

A thread portion 10 is formed on an inner surface of the main portion 8for threaded engagement with a male screw 22 formed on an outer surface21 c of the container mouth portion 21.

Tabs 11 that are locking means to prevent movement of the TE ringportion 9 by locking with a bulging step portion 23 on the containermouth portion 21 when opening the cap 1 are provided on an inner wallsurface of the TE ring portion 9. The tabs 11 are formed in a plateshape that may rise and fall.

As shown in FIG. 2 and FIG. 3, an annular inside seal projection 12 thatis fitted into the container mouth portion 21 is protrudingly formedfacing downward on an inner surface 2 a of the top plate portion 2.

An annular abutting convex portion 12 a that abuts a container innersurface 21 a is formed on an outer surface of a tip of the inside sealprojection 12.

The inside seal projection 12 is formed so that when fit in thecontainer mouth portion 21 a maximum outer diameter portion 12 d of theabutting convex portion 12 a abuts the container inner surface 21 awithout clearances to be able to tightly seal the container mouthportion 21.

The outer diameter of the maximum outer diameter portion 12 d ispreferably set to be slightly greater than the inner diameter of thecontainer mouth portion 21.

An opening end seal projection 13 that abuts an opening end face 21 b ofthe container mouth portion 21 and an outside seal projection 14 thatabuts the outer surface 21 c of the container mouth portion 21 areformed on the top plate portion 2 outward of the inside seal projection12.

A connector portion 15 that couples the top plate portion 2 and theinside seal projection 12 is formed between the inner surface 2 a of thetop plate portion 2 and the inner surface 12 b of the inside sealprojection 12.

The connector portion 15 firmly fixes the inside seal projection 12 tothe top plate portion 2 and maintains a constant angle of the insideseal projection 12 with respect to the top plate portion 2.

In the example illustrated, the connector portion 15 is a substantiallytriangular plate nearly perpendicular to the top plate portion 2 formedin the radial direction. A top edge portion 15 a of the connectorportion 15 is integrally fixed to the top plate portion inner surface 2a, and a side edge portion 15 b is integrally fixed to the inner surface12 b of the inside seal projection. An inner edge portion 15 c of theconnector portion 15 preferably has a shape descending gradually asoutwardly.

It is preferable for the connector portion 15 to be integrally formedwith the top plate portion 2 and the inside seal projection 12.

As shown in FIG. 2, it is preferable for a height A of the connectorportion 15 to be 0.5 mm to 5 mm (preferably 1 mm to 4 mm).

When the height A is less than the aforementioned range, discharge ofthe gas in the container 20 is hindered when the internal pressurerises. When the height A exceeds the aforementioned range, deformationof the inside seal projection 12 is hindered when fitted into thecontainer mouth portion 21, thereby losing the ease of the closingoperation. In addition, the mold releasability at forming worsens.

It is preferable for a width B in the radial direction of the connectorportion 15 to be 0.1 to 3 mm (preferably 0.3 mm to 1 mm).

When the width B is less than the aforementioned range, discharge of thegas in the container 20 is hindered when the internal pressure rises.When the width B exceeds the aforementioned range, deformation of theinside seal projection 12 is hindered when fitted into the containermouth portion 21, thereby losing the ease of the closing operation. Inaddition, the mold releasability at forming worsens.

The connector portion is not limited to the illustrated shape, and maybe made into an optional shape such as a square plate shape, fan plateshape, rectangular shape, and pyramid shape.

As shown in FIG. 4, it is preferable for the connector portion 15 to beformed not along the entire circumference of the top plate portion 2 andthe inside seal projection 12, but only in partly portions in thecircumferential direction.

In the illustrated example, the connector portions 15 are provided infour places spaced out in the circumferential direction. The connectorportions 15 are provided so that the distances between the two mutuallyadjacent connector portions 15 are roughly equivalent.

It is preferable for the number of the connector portions 15 to beformed to be 1 to 6 (preferably 1 to 4).

Having the number of connector portions 15 in this range causes theaforementioned tensile force to act on the inside seal projection 12biased in the circumferential direction, thereby facilitatingdeformability of the inside seal projection 12 inward. Accordingly, whenthe internal pressure of the container rises, the gas in the container20 may be easily discharged to the outside.

When the formed number exceeds the aforementioned range, deformation ofthe inside seal projection 12 is hindered when the internal pressure ofthe container rises, thereby hindering the discharge of the gas in thecontainer 20.

As shown in FIG. 2, an annular thin concave portion 16 a is formed onthe bottom surface of the top plate portion 2 between the portion 12 cwhere the inside seal projection 12 is formed and the portion 13 a wherethe open end seal projection 13 is formed. The portion of the top plateportion 2 where the thin concave portion 16 a is formed is an outsidethin wall portion 16 formed thinner than the circumferential edgeportion 2 b and the outer circumferential side portion 17.

The outside thin wall portion 16 is formed in an adjacent positionoutward of the portion 12 c where the inside seal projection 12 isformed.

The outside thin wall portion may be formed at any position between theportion 12 c where the inside seal projection 12 is formed and thecircumferential edge portion 2 b, with the forming position thereof notlimited by the illustrated example. In addition, the outside thin wallportion may be formed by a thin concave portion provided on the topsurface of the top plate portion.

The outside thin wall portion 16 is formed so that a thickness C thereofis less than a thickness D of the circumferential edge portion 2 b ofthe top plate portion 2.

When the thickness C of the outside thin wall portion 16 is equal to orgreater than the thickness D of the circumferential edge portion 2 b,discharge of the gas in the container 20 is hindered when the internalpressure of the container rises.

It is preferable for the thickness C of the outside thin wall portion 16to be 0.3 mm to 2 mm (preferably 0.5 mm to 1.5 mm).

Having the thickness C in the aforementioned range facilitates bendingdeformation of the outside thin wall portion 16, bulging deformation ofthe top plate portion 2 at the portion corresponding to the inside ofthe inside seal projection 12, and discharge of the gas in the container20 when the internal pressure of the container rises.

When the thickness C is less than the aforementioned range, the strengthof the outside thin wall portion 16 becomes too low, and when it exceedsthis range discharge of the gas in the container 20 is hindered when theinternal pressure of the container rises.

It is preferable for the thickness C of the outside thin wall portion 16to be set to a value corresponding to 0.3 to 0.9 times the thickness Dof the circumferential edge portion 2 b. When the thickness C is lessthan this range, the strength of the outside thin wall portion 16becomes too low, and when it exceeds this range, discharge of the gas inthe container 20 is hindered when the internal pressure of the containerrises.

It is desirable for the thickness D of the top plate portion 2 at thecircumferential edge portion 2 b be 0.5 mm to 3 mm (preferably 0.8 mm to2 mm).

The top plate portion 2 at the portion corresponding to the inside ofthe inside seal projection 12 has an outer circumferential portion 17where the connector portion 15 is formed and an inner circumferentialportion 18.

It is desirable for a thickness E of the outer circumferential portion17 be 0.5 mm to 3 mm (preferably 0.8 mm to 2 mm).

Having the thickness E in the aforementioned range may impart sufficientstrength to this portion. Consequently, the action that displaces theinside seal projection 12 by the connector portion 15 when the pressurein the container increases is enhanced, which may facilitate dischargeof the gas in the container 20.

When the thickness E is less than the aforementioned range, the strengthof the top plate portion 2 becomes too low, the action that displacesthe inside seal projection 12 by the connector portion 15 diminishes,and so the discharge of the gas in the container 20 is hindered when theinternal pressure of the container rises. When the thickness E exceedsthis range, bulging deformation of the top plate portion 2 is hindered,and so the discharge of the gas in the container 20 is hindered when theinternal pressure of the container rises.

It is preferable for a width F of the outer circumferential portion 17to be 0.5 mm to 10 mm (preferably 2 mm to 7 mm).

Having the width F in the aforementioned range enhances the action thatdisplaces the inside seal projection 12 by the connector portion 15, andmay thereby facilitate the discharge of the gas in the container 20 tothe outside when the internal pressure of the container rises.

When the width F is less than the aforementioned range, the action thatdisplaces the inside seal projection 12 due to the connector portion 15diminishes, hindering discharge of the gas in the container 20 when theinternal pressure of the container rises. When the width F exceeds theaforementioned range, bulging deformation of the top plate portion 2 ishindered, and so the discharge of the gas in the container 20 ishindered when the internal pressure of the container rises.

A thinned concave portion 18 a is formed on the inner surface of theinner circumferential portion 18. Thereby, the inner circumferentialportion 18 becomes the inside thin wall portion 18 b formed thinner thanthe outer circumferential portion 17. As shown in the illustratedembodiments of FIGS. 1-3, the outer circumferential side portion 17 andthe inside thin wall portion 18 b have a substantially constantthickness. The thinned concave portion 18 a is preferably circular.

It is desirable for a thickness G of the inside thin wall portion 18 bto be 0.3 mm to 2 mm (preferably 0.5 mm to 1.5 mm).

Having the thickness G in the aforementioned range facilitates bulgingdeformation of the top plate portion 2, whereby displacement of theinside seal projection 12 occurs easily. Consequently, discharge of thegas in the container 20 is facilitated when the internal pressure of thecontainer rises.

When the thickness G is less than the aforementioned range, the strengthof the inside thin wall portion 18 b becomes too low, thereby degradingthe durability of the cap 1. When the thickness G exceeds this range,bulging deformation of the top plate portion 2 is hindered, and sodischarge of the gas is hindered when the internal pressure of thecontainer rises.

In the illustrated example, the entire inner circumferential portion 18assumes the inside thin wall portion 18 b formed thinner than the outercircumferential portion 17, but in the present invention, only a portionof the inner circumferential portion 18 may be thinned. To wit, theannular thinned concave portion may be formed at only the portion nearthe circumferential edge of the inner circumferential portion 18, andthis annular portion may serve as the inside thin wall portion.

It is preferred for the height of the maximum outer diameter portion 12d of the inside seal projection 12 to be set so that a difference inheight H between the maximum outer diameter portion 12 d and the bottomend of the open end seal projection 13 is 1 mm to 4 mm (preferably 1.5mm to 3 mm).

Having the difference in height H in the aforementioned range mayfacilitate discharge of the gas in the container when the internalpressure of the container rises and enhance tamper evidence.

When the difference in height H is less than the aforementioned range,displacement of the inside seal projection 12 is hindered during bulgingdeformation of the top plate portion 2 when the internal pressure of thecontainer rises, thereby hindering discharge of the gas in thecontainer. It is also not preferred from the aspect of tamper evidencebecause seal breakage during the opening process occurs earlier.

When the difference in height H exceeds the aforementioned range, theseal breakage during the opening process is delayed, giving rise to therisk of the cap 1 readily coming off by the internal pressure of thecontainer.

It is preferable that the protruding height of the outside sealprojection 14 be set so that a difference in height I between the bottomend of the projection 14 and the bottom end of the opening end sealprojection 13 is 3 mm or less (preferably 1.5 mm or less).

Having the difference in height I in the aforementioned rangefacilitates discharge of the gas in the container when the internalpressure of the container rises.

When the difference in height I exceeds this range, detachment of theoutside seal projection 14 from the container mouth portion 21 ishindered during bulging deformation of the top plate portion 2 when theinternal pressure of the container rises, and thereby hinders dischargeof the gas from inside the container.

In consideration of the sealing property, it is preferred that thedifference in height I be set so as to be not less than 0.2 mm(preferably not less than 0.3 mm).

The cross-sectional radius of curvature of a junction portion 19 that isthe portion where the top plate portion 2 and the cylinder portion 3 arejoined is preferably not less than 0.6 mm (preferably not less than 0.8mm).

Having the radius of curvature in the aforementioned range increases thestrength of the junction portion 19, which may hinder displacement ofthe top plate portion 2 at the portion corresponding to the outside ofthe outside thin wall portion 16 when the internal pressure of thecontainer rises.

Consequently, the top plate portion 2 at the portion corresponding tothe inside of the outside thin wall portion 16 is greatly bulged and theslope of the top plate portion 2 at the portion 12 c where the insideseal projection 12 is formed is increased, facilitating inwarddisplacement of the inside seal projection 12. Accordingly, discharge ofthe gas in the container is facilitated.

When the radius of curvature less than the aforementioned range, inwarddisplacement of the inside seal projection 12 is hindered, therebyhindering the discharge of the gas in the container.

The aforementioned radius of curvature is preferably not more than 2 mm.When the radius of curvature exceeds the aforementioned range,separation of the opening end seal projection 13 and the outside sealprojection 14 from the container mouth portion 21 is hindered, therebyhindering the discharge of the gas in the container.

A distance J between an inner surface 3 a of the cylinder portion 3(base end of the thread portion 10) and the male screw 22 when the cap 1is attached to the container mouth portion 21 is preferably not morethan 1 mm (preferably 0.1 mm to 0.5 mm).

Having the distance J in the aforementioned range enhances the holdingpower of the cap 1 with respect to the container mouth portion 21, whichmay prevent the cap 1 from coming off the container mouth portion 21when opening.

When the distance J is less than the aforementioned range, attachment ofthe cap 1 to the container mouth portion 21 may be hindered. When thedistance J exceeds the aforementioned range, the cap 1 readily comes offthe container mouth portion 21 during opening.

A distance K between the tip of the thread portion 10 and the outersurface 21 c of the container mouth portion 21 is preferably not morethan 1 mm (preferably 0.1 mm to 0.5 mm).

Having the distance K in the aforementioned range enhances the holdingpower of the cap 1 with respect to the container mouth portion 21, whichmay prevent the cap 1 from coming off the container mouth portion 21when opening.

When the distance K is less than the aforementioned range, attachment ofthe cap 1 to the container mouth portion 21 may be hindered. When thedistance K exceeds the aforementioned range the cap 1 readily comes offthe container mouth portion 21 during opening.

The synthetic resin material constituting the cap 1 may include amaterial containing polypropylene or polyethylene.

It is preferable that the flexural modulus of the top plate portion 2 be500 to 2,000 MPa (preferably 1,000 to 1,800 MPa).

Having the flexural modulus in the aforementioned range may facilitatedischarge of the gas in the container when the internal pressure of thecontainer is increased and prevent breakage of the cap 1. Doing so alsoenhances the holding power with respect to the container mouth portion21, which may prevent the cap 1 from readily coming off during opening.

When the flexural modulus is less than the aforementioned range,cracking readily occurs in the top plate portion 2.

When the flexural modulus exceeds the aforementioned range, displacementof the inside seal projection 12 is hindered when the internal pressureof the container is increased, thereby hindering discharge of the gas inthe container. Also, the cap 1 readily comes off during opening.

It is preferable for the density of the material constituting the cap 1to be 0.85 to 0.97 g/cm³ (preferably 0.87 to 0.95 g/cm³).

Having the density in the aforementioned range may facilitate dischargeof the gas in the container when the internal pressure of the containeris increased and may prevent breakage of the cap 1. Doing so alsoenhances the holding power with respect to the container mouth portion21, which may prevent the cap 1 from readily coming off during opening.

When the density is less than the aforementioned range, displacement ofthe inside seal projection 12 is hindered when the internal pressure ofthe container is increased, thereby hindering discharge of the gas inthe container. Also, the cap 1 readily comes off during opening. Whenthe density exceeds the aforementioned range, cracking readily occurs inthe cap 1.

Below, the method of using the cap 1 is explained referring to FIG. 3and FIG. 5.

The cap 1 is attached to the mouth portion 21 of the container 20 filledwith a content liquid as shown in FIG. 3. At this time, the inside sealprojection 12 is inserted in the container mouth portion 21.

The inside seal projection 12 abuts the container inner surface 21 a atthe abutting convex portion 12 a, sealing this portion. By doing so thecontainer 20 is hermetically sealed.

In this hermetically sealed state (when unopened), the opening end sealprojection 13 abuts the opening end face 21 b and the outside sealprojection 14 abuts the container outer surface 21 c.

Also, the tabs 11 provided on the TE ring portion 9 surmount the annularbulging step portion 23 provided directly under the male screw 22,reaching below the bulging step portion 23.

When the cap 1 attached to the container mouth portion 21 is rotated inthe opening direction, the cap 1 rises, the inside seal projection 12 ispulled out of the container mouth portion 21, and the hermetic seal ofthe container 20 is broken.

Because at this time the tabs 11 provided on the inner surface of the TEring portion 9 lock with the lower portion of the bulging step portion23, while the main portion 8 rises in accordance with the rotation,upward movement of the TE ring portion 9 is blocked. Consequently,tensile force acts on the bridge 7 connecting the main portion 8 and TEring portion 9 of the cap 1, by which the bridges 7 break, and the TEring portion 9 is detached from the main portion 8. By detaching the TEring portion 9, it is evident that the cap 1 is opened.

When the cap 1 is opened and then recapped, the internal pressure of thecontainer 20 may rise considerably (for example, 0.4 MPa or more) due tofermentation of the content liquid and the like.

When the pressure in the container 20 rises, upward force acts on thetop plate portion 2 due to the internal pressure of the container.

As shown in FIG. 5, applying force upwardly to the top plate portion 2from the internal pressure of the container causes upward bulgingdeformation (so-called doming) of the top plate portion 2.

Along with the bulging deformation of the top plate portion 2, top edgeportions 15 a of the connector portions 15 are displaced upward, and asa result, tensile force is applied inwardly on the inside sealprojection 12 by the connector portions 15.

The bulging deformation of the top plate portion 2 causes the centerportion thereof to rise. Whereby, the top plate portion 2 assumes asloped state descending gradually from the center portion thereofheading outward.

Because the strength of the top plate portion 2 is lower at the outsidethin wall portion 16, when an upward force is applied on the top plateportion 2 from the internal pressure of the container, the top plateportion 2 undergoes bending deformation at the outside thin wall portion16, and the portion inward of the outside thin wall portion 16 undergoessignificant bulging deformation upward.

Due to the slope of the top plate portion 2 during bulging deformation(the slope with respect to the top plate portion 2 when undeformed)being greater nearer the circumferential edge of the deformed portion,the slope of the top plate portion 2 inward of the outside thin wallportion 16 is greater nearer the outside thin wall portion 16.

Consequently, the slope of the top plate portion 2 at the portion 12 cwhere the inside seal projection 12 is formed increases compared to thecase of the entire top plate-portion 2 deformably swelling.

Moreover, due to the strength of the junction portion 19 beingsufficiently raised by its cross-sectional radius of curvature beingwithin the aforementioned range, the top plate portion 2 at the portioncorresponding to the outside of the outside thin wall portion 16 ishindered from deforming upward.

Consequently, the portion positioned inward of the outside thin wallportion 16 deformably swells upward to a greater extent, and the slopeof the top plate portion 2 at the portion 12 c where the inside sealprojection 12 is formed further increases.

In this way, due to inward tensile force being applied to the insideseal projection 12 by the connector portions 15 and the top plateportion 2 (the portion 12 c where the inside seal projection 12 isformed) greatly sloping, at least a portion of the inside sealprojection 12 is displaced in the direction of inward movement of thetip, and the abutting convex portion 12 a separates from the containerinner surface 21 a.

This causes the gas in the container 20 to be discharged to the outsidethrough the gap between the container inner surface 21 a and the insideseal projection 12.

The aforementioned cap 1 exhibits the following effects:

(1) By having connector portions 15 formed between the top plate portion2 and the inside seal projection 12, sloping of the top plate portion 2by bulging deformation due to rising of the internal pressure of thecontainer causes inward tensile force to be applied to the inside sealprojection 12.

Also, because the outside thin wall portion 16 is formed on the topplate portion 2, the top plate portion 2 undergoes bending deformationat the outside thin wall portion 16, causing the portion positionedinside the outside thin wall portion 16 to undergo significant bulgingdeformation upward.

Because of this, the slope of the top plate portion 2 at the portion 12c where the inside seal projection 12 is formed increases compared tothe case of the entire top plate portion 2 deformably swelling.

Consequently, the inside seal projection 12 is displaced in thedirection of inward movement of the tip, facilitating discharge of thegas in the container 20 through the gap between the container innersurface 21 a and the inside seal projection 12.

Accordingly, the cap 1 may prevent an excessive increase in the internalpressure of the container 20 after recapping.

In the case of the outside thin wall portion 16 not being formed, whenthe internal pressure of the container rises, because the entire topplate portion 12 deformably swells, the slope of the portion 12 b wherethe inside seal projection 12 is formed is lessened, thereby hinderinginward displacement of the inside seal projection 12. Accordingly,discharge of the gas in the container 20 is hindered.

(2) Having the cross-sectional radius of curvature of the junctionportion 19 in the aforementioned range sufficiently raises the strengthof the junction portion 19, which may thereby hinder displacement of thetop plate portion 2 at the portion corresponding to outside of theoutside thin wall portion 16.

For this reason, the portion positioned inward of the outside thin wallportion 16 deformably swells upward to a greater extent, and so theslope of the top plate portion 2 at the portion 12 c where the insideseal projection 12 is formed may be further increased.

Accordingly, an excessive increase in the internal pressure of thecontainer may be surely prevented after recapping.

(3) Since the connector portion 15 is formed only in a portion of thecircumferential direction, the inward tensile force acts locally only ona portion of the inside seal projection 12.

Since the tensile force acts on the inside seal projection 12 biased inthe circumferential direction, the strain produced in the inside sealprojection 12 by inward displacement of the inside seal projection 12 atthe portions where the connector portion 15 are formed is absorbed bythe portions where the connector portions 15 are not formed.

Consequently, the inside seal projection 12 at the portion where thetensile force acts is easily displaced inward, compared to the case ofthe connector portion being formed over the entire circumference.

(4) A common method of sterilizing the inside of a cap is to run hotwater over the outer surface of the cap attached to a container mouthportion.

As shown in FIG. 3, since in the cap 1 the outside thin wall portion 16is formed in the top plate portion 2, by supplying hot water to theouter surface of the top plate portion 2, sufficient heat can betransmitted through the outside thin wall portion 16 to an inner space L(the space surrounded by the inner seal projection 12, the top plateportion 2, the opening end seal projection 13 and the container mouthportion 21).

Accordingly, the inner space L may be surely sterilized.

By filling a beverage such as juice, tea or coffee in the container 20and attaching the cap 1 to the mouth portion 21, a container-packedbeverage filled with the beverage may be provided with theaforementioned closing device.

INDUSTRIAL APPLICABILITY

The synthetic resin cap of the present invention exhibits the followingeffects:

(1) By having connector portions formed between the top plate portionand the inside seal projection, sloping of the top plate portion bybulging deformation due to rising of the internal pressure of thecontainer causes inward tensile force to be applied to the inside sealprojection.

Also, because the outside thin wall portion is formed on the top plateportion, the top plate portion undergoes bending deformation at theoutside thin wall portion, causing the portion positioned inside theoutside thin wall portion to undergo significant bulging deformationupward.

Because of this, the slope of the top plate portion at the portion wherethe inside seal projection is formed increases.

Consequently, the inside seal projection is displaced in the directionof inward movement of the tip and separates from the container innersurface, thereby facilitating the discharge of the gas in the containerto the outside.

Accordingly, an excessive increase in the internal pressure of thecontainer may be prevented after recapping.

(2) Having the cross-sectional radius of curvature of the junctionportion in the aforementioned range sufficiently raises the strength ofthe junction portion, which may thereby hinder displacement of the topplate portion at the portion corresponding to the outside of the outsidethin wall portion.

For this reason, the portion positioned inward of the outside thin wallportion deformably swells upward to a greater extent, and so the slopeof the top plate portion at the portion where the inside seal projectionis formed may be further increased.

Accordingly, an excessive increase in the internal pressure of thecontainer may be surely prevented after recapping.

1. A synthetic resin cap comprising: a cap body having a top plateportion and a cylinder portion hanging from a circumferential edgeportion thereof; an annular inside seal projection to be fitted into acontainer mouth portion formed on an inner surface of the top plateportion; a connector portion that connects the top plate portion and theinside seal projection formed between the inner surface of the top plateportion and an inner surface of the inside seal projection; an outsidethin wall portion which is thinner than the circumferential edge portionformed on the top plate portion at any position between a portion wherethe inside seal projection is formed and the circumferential edgeportion; wherein the top plate portion at the portion corresponding tothe inside of the inside seal projection has an outer circumferentialside portion where the connector portion is formed, and an inside thinwall portion that is formed on the inside of the outer circumferentialside portion; and wherein the cap further comprises a first transitionsection that transitions from the annular inside seal projection to theouter circumferential side portion in a radially inward direction and asecond transition section that transitions from the outercircumferential side portion to the inside thin wall portion in aradially inward direction, wherein the inside thin wall portion isthinner than the outer circumferential side portion, which is thinnerthan the annular inside seal projection in a direction perpendicular tothe top plate.
 2. The synthetic resin cap according to claim 1, wherein:a cross-sectional radius of curvature at the inner surface side of ajunction portion of the top plate portion and the cylinder portion isnot less than 0.6 mm; a thickness of the outer circumferential sideportion is 0.5 mm to 3 mm; a width of the outer circumferential sideportion is 0.5 mm to 10 mm; an opening end seal projection to abut anopening end face of the container mouth portion is formed on the topplate portion; and an outside seal projection to abut an outer surfaceof the container mouth portion is formed on the top plate portion. 3.The synthetic resin cap according to claim 1, wherein when attached tothe container mouth portion, a distance between an inner surface of thecylinder portion and a tip of a male screw formed on an outer surface ofthe container mouth portion is not more than 1 mm.
 4. The syntheticresin cap according to claim 1, wherein when attached to the containermouth portion, a distance between a tip of a thread portion formed inthe cylinder portion and the outer surface of the container mouthportion is not more than 1 mm.
 5. The synthetic resin cap according toclaim 2, wherein: the inside seal projection is made to abut an innersurface of the container mouth portion at a maximum outer diameterportion; and the height position of the maximum outer diameter portionis set so that a difference in height of the maximum outer diameterportion and a bottom end of the opening end seal projection is 1 mm to 4mm.
 6. The synthetic resin cap according to claim 2, wherein the outsideseal projection is formed so that the difference in height of a bottomend of this projection and the bottom end of the opening end sealprojection is not more than 3 mm.
 7. The synthetic resin cap accordingto claim 2, wherein the flexural modulus of the top plate portion is 500to 2,000 MPa.
 8. The synthetic resin cap according to claim 2, whereinthe density of the material constituting the synthetic resin cap is 0.85to 0.97 g/cm³.
 9. The synthetic resin cap according to claim 1, whereina thickness of the inside thin wall portion is thinner than a thicknessof the circumferential edge portion of the top plate portion.
 10. Thesynthetic resin cap according to claim 1, wherein the outside thin wallportion has a thickness of 0.3 mm to 2 mm.
 11. The synthetic resin capaccording to claim 1, wherein the outside thin wall portion is a thinconcave portion provided on a top surface of the top plate portion. 12.The synthetic resin cap according to claim 1, wherein the transitionportion of the outer circumferential side portion is tapered.
 13. Thesynthetic resin cap according to claim 1, wherein the transition portionof the inside thin wall portion is tapered.
 14. The synthetic resin capaccording to claim 1, wherein the transition portion of the outercircumferential side portion and the transition portion of the insidethin wall portion are tapered.
 15. The synthetic resin cap according toclaim 1, wherein each of the non-tapered portion of the outercircumferential side portion and the non-tapered portion of the insidethin wall portion has a constant thickness.